The most prominent GPL project is Linux, the kernel of an operating system that will underlie a $35.7bn business in 2008, according to a forecast by market researcher IDC. Among others: the MySQL database, the netfilter/iptables protective firewall and the Samba file-sharing software.
But programmers have other choices if they're not happy with the GPL. Other licences cover the Mozilla project, which helped launch the open source movement in 1998, and the widely used Apache server software. And Sun is testing its Community Development and Distribution License, which likely will be used to govern its Solaris version of Unix.
The patent problem
Patents are one reason Sun chose the licence it did. How the GPL deals with that thorny legal area is the issue more than a dozen experts raised most often in discussions for this story.
The patent problems boil down to two issues. First, should the licence explicitly require those who distribute GPL software to grant others unhindered use of whatever patented technology is involved in that software? And second, should there be some form of punishment for those who file lawsuits alleging that GPL software infringes their patents?
These issues are under discussion for the next version of the GPL. "It may possibly help protect our community from pirates armed with patents," says Stallman, a critic of the overall idea of software patents.
One interpretation of the current GPL is that patent holders who distribute GPL software "are in effect granting an implied licence" to those patents, says Mark Webbink, the lead intellectual-property attorney for Red Hat and a person who first saw revised GPL drafts in 2000. But it might be useful to have an explicitly expressed patent agreement, he said. "A distributor may not want to leave that ambiguous as to what rights they are giving."
